libsnapshot: Add SnapshotManagerStub.

Avoid crashes in update_engine. When SnapshotManager
should not be used (e.g. Virtual A/B is not enabled),
use the stub instead.

Bug: 148956645
Test: update_engine_unittests
Change-Id: Id524a1dfe5d085d439fc5492d4b7f72ee583c17e

3 files changed, 163 insertions, 0 deletions

diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index bd788f5a9..0403031e8 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -73,6 +73,7 @@ filegroup {
         "device_info.cpp",
         "snapshot.cpp",
         "snapshot_stats.cpp",
+        "snapshot_stub.cpp",
         "snapshot_metadata_updater.cpp",
         "partition_cow_creator.cpp",
         "return.cpp",
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h
new file mode 100644
index 000000000..924f26d49
--- /dev/null
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h
@@ -0,0 +1,51 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <libsnapshot/snapshot.h>
+
+namespace android::snapshot {
+
+class SnapshotManagerStub : public ISnapshotManager {
+  public:
+    // Create a stubbed snapshot manager. All calls into the stub fails.
+    static std::unique_ptr<ISnapshotManager> New();
+
+    // ISnapshotManager overrides.
+    bool BeginUpdate() override;
+    bool CancelUpdate() override;
+    bool FinishedSnapshotWrites(bool wipe) override;
+    bool InitiateMerge() override;
+    UpdateState ProcessUpdateState(const std::function<bool()>& callback = {},
+                                   const std::function<bool()>& before_cancel = {}) override;
+    UpdateState GetUpdateState(double* progress = nullptr) override;
+    Return CreateUpdateSnapshots(
+            const chromeos_update_engine::DeltaArchiveManifest& manifest) override;
+    bool MapUpdateSnapshot(const android::fs_mgr::CreateLogicalPartitionParams& params,
+                           std::string* snapshot_path) override;
+    bool UnmapUpdateSnapshot(const std::string& target_partition_name) override;
+    bool NeedSnapshotsInFirstStageMount() override;
+    bool CreateLogicalAndSnapshotPartitions(
+            const std::string& super_device,
+            const std::chrono::milliseconds& timeout_ms = {}) override;
+    bool HandleImminentDataWipe(const std::function<void()>& callback = {}) override;
+    CreateResult RecoveryCreateSnapshotDevices() override;
+    CreateResult RecoveryCreateSnapshotDevices(
+            const std::unique_ptr<AutoDevice>& metadata_device) override;
+    bool Dump(std::ostream& os) override;
+    std::unique_ptr<AutoDevice> EnsureMetadataMounted() override;
+};
+
+}  // namespace android::snapshot
diff --git a/fs_mgr/libsnapshot/snapshot_stub.cpp b/fs_mgr/libsnapshot/snapshot_stub.cpp
new file mode 100644
index 000000000..6c82f61ee
--- /dev/null
+++ b/fs_mgr/libsnapshot/snapshot_stub.cpp
@@ -0,0 +1,111 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <libsnapshot/snapshot_stub.h>
+
+#include <android-base/logging.h>
+
+using android::fs_mgr::CreateLogicalPartitionParams;
+using chromeos_update_engine::DeltaArchiveManifest;
+
+namespace android::snapshot {
+
+std::unique_ptr<ISnapshotManager> SnapshotManagerStub::New() {
+    return std::make_unique<SnapshotManagerStub>();
+}
+
+bool SnapshotManagerStub::BeginUpdate() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::CancelUpdate() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::FinishedSnapshotWrites(bool) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::InitiateMerge() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+UpdateState SnapshotManagerStub::ProcessUpdateState(const std::function<bool()>&,
+                                                    const std::function<bool()>&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return UpdateState::None;
+}
+
+UpdateState SnapshotManagerStub::GetUpdateState(double*) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return UpdateState::None;
+}
+
+Return SnapshotManagerStub::CreateUpdateSnapshots(const DeltaArchiveManifest&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return Return::Error();
+}
+
+bool SnapshotManagerStub::MapUpdateSnapshot(const CreateLogicalPartitionParams&, std::string*) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::UnmapUpdateSnapshot(const std::string&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::NeedSnapshotsInFirstStageMount() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::CreateLogicalAndSnapshotPartitions(const std::string&,
+                                                             const std::chrono::milliseconds&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::HandleImminentDataWipe(const std::function<void()>&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+CreateResult SnapshotManagerStub::RecoveryCreateSnapshotDevices() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return CreateResult::ERROR;
+}
+
+CreateResult SnapshotManagerStub::RecoveryCreateSnapshotDevices(
+        const std::unique_ptr<AutoDevice>&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return CreateResult::ERROR;
+}
+
+bool SnapshotManagerStub::Dump(std::ostream&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+std::unique_ptr<AutoDevice> SnapshotManagerStub::EnsureMetadataMounted() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return nullptr;
+}
+
+}  // namespace android::snapshot